The present invention relates in general to the art of earth boring and more particularly to an improved bearing for a rotary rock bit. The present invention is especially adapted for use on that type of rotary rock bit popularly known as a three cone bit; however, its use is not restricted thereto and the bearing system of the present invention can be used in other earth boring equipment wherein an improved bearing is needed.
A three cone rotary rock bit is adapted to be connected as the lower member of a rotary drill string. As the drill string is rotated the bit disintegrates the formations to form an earth borehole. The three cone rotary rock bit includes three individual arms that extend angularly downward from the main body of the bit. The lower end of each arm is shaped to form a bearing pin or journal. A cone is mounted upon each bearing pin (or journal) and adapted to rotate thereon. The cones include cutting structure on their outer surface that serves to disintegrate the formations as the bit is rotated.
A rotary rock bit must operate under very severe environmental conditions and the size and geometry of the bit is restricted by the operating characteristics. At the same time, the economics of petroleum production demand a longer lifetime and improved performance from the bit. In attempting to provide an improved bit, new and improved materials have been developed for the cutting structure of the cones thereby providing a longer useful lifetime for the cones. This has resulted in the bearing and/or sealing systems being generally the first to fail during the drilling operation. Consequently, a need exists for an improved bearing system to extend the useful lifetime of the bit.
Friction and anti-friction bearings, as well as a combination of friction and anti-friction bearings, have been used in rotary rock bits. The anti-friction bearings employed have been typically a set of rollers and a set of balls positioned in mating raceways in the cone and bearing pin. Certain disadvantages are associated with anti-friction bearings. For example, the space required to accommodate the rollers and balls is obtained only by sacrificing bearing pin metal, cone shell thickness, or a combination of both. Certain disadvantages are also associated with friction bearings used in rotary rock bits. It is generally necessary to have a friction bearing length to diameter ratio of greater than two and one-half when operating under severe conditions. The size limitations of a rotary rock bit make it substantially impossible to provide this desired ratio and friction bearings used in rock bits encounter severe operating conditions.
Friction bearings in prior art rock bits have used either carburized surfaces or carburized surfaces interspersed with anti-galling material placed in grooves or slots at uniform or random intervals. Bare carburized bearing surfaces are totally dependent on lubricant performance. Carburized bearing surfaces interspersed with metallic anti-galling material at best provide the load area of the bearing with intermittent access to the anti-galling material, or only provide a small portion of the bearing load area with anti-galling material at any one instant.